Semiconductor lasers have many advantages, such as the small size, inexpensiveness, low power consumption and long life. Due to those advantages, semiconductor lasers have 15 been popularly used in a wide range of areas, such as light sources for optical recording, light sources for communications, laser displays, laser printers, or laser pointers. In the area of the laser-beam machining, a laser whose optical output exceeds at least 1 W is needed. However, none of the semiconductor lasers practically used so far have reached this output level. Accordingly, gas lasers, such as a carbon dioxide gas laser, have been used for this purpose.
In recent years, a two-dimensional photonic-crystal surface-emitting laser whose optical output exceeds the level of 1 W has been developed by Noda et al., who are members of the group of the present inventors (Non Patent Literatures 1 and 2). A two-dimensional photonic-crystal surface-emitting laser includes an active layer, a two-dimensional photonic 25 crystal, and a pair of electrodes between which the two previously mentioned elements are sandwiched. The two-dimensional photonic crystal is a device including a plate-shaped base body in which modified refractive index areas whose refractive index differs from that of the base body are periodically arranged, thereby forming a periodic distribution of the refractive index. An injection of electric current from the electrodes into the two-dimensional photonic-crystal surface-emitting laser induces an emission of light in the active layer. In this light, only a specific wavelength of light corresponding to the periodicity of the modified refractive index areas is amplified and causes a laser oscillation, to be eventually emitted as a laser beam in a perpendicular direction to the two-dimensional photonic crystal. This light is emitted from a certain region within the two-dimensional photonic crystal (surface emission). Accordingly, two-dimensional photonic-crystal surface-emitting lasers have a larger emission area than conventional semiconductor lasers and their optical output can be more easily increased. Two-dimensional photonic-crystal surface-emitting lasers themselves have already been known (for example, see Patent Literature 1). A feature of the invention described in Non Patent Literatures 1 and 2 exists in that modified refractive index areas having a right-triangular planar shape are arranged at the lattice points of a square lattice in such a manner that the orthogonally intersecting sides of the right triangle are parallel to the lattice. With this device, the optical output can be increased to approximately 1.5 W.